It's just a matter of saving a node, in case I'm going to have many instances of the scene requesting the invoke_later(). But at the moment I don't care that much, so I'll take the option requiring the less work :)

1) You can add a timer, and run the function when it times out.
2) you can set up a couple variables of your own to hold the time and a value to check against time out and make your own accumulator (either in frames or by accumulating delta)